This invention relates generally to supercapacitor desalination (SCD) cells, devices and methods. More particularly, this invention relates to supercapacitor desalination cells, devices and methods using ion selective layers.
SCD devices generally refer to supercapacitors that are employed for desalination of seawater or deionization of other brackish waters to reduce the amount of salt to a permissible level for domestic and industrial use. Generally, a supercapacitor desalination cell has a double layer construction, in which a pair of electrodes typically comprising particulate activated carbon or other conductive high surface area materials are separated by a spacer. The structure of the typical supercapacitor cell further comprises electrically conductive current collector elements in intimate contact with the respective electrodes.
In certain applications, the supercapacitor desalination cells employ a plurality of ion selective layers in intimate contact with respective electrodes to facilitate adsorption and desorption of cations and anions in electrolytes to and from the electrodes when such supercapacitor desalination cells are in charging and discharging states, respectively. However, in current applications, the ion selective layers have more selectivity for polyvalent ions than to monovalent ions since the polyvalent ions generally have higher polarities than those of the monovalent ions, which is disadvantageous for removal of the monovalent ions.
Additionally, when calcium cations and magnesium cations are selectively removed, divalent ions are preferentially attracted to the electrodes via the respective ion selective layers causing high concentrations of Ca2+ and Mg2+, and high concentrations of SO42− and CO32− at respective electrodes. This causes decrease of pH values in surfaces of cathodes, such as carbon cathodes during charging resulting in scale formation within the electrodes, and/or between the electrodes and the ion selective layers.
Therefore, there is a need for new and improved supercapacitor desalination cells, devices and methods equipped with ion selective layers for removal of one or more monovalent ions and avoiding scale formation within the supercapacitor desalination cells and devices.